The most common axicon is a flat cone. A small source of light on the axis of the cone is imaged into a line along a portion of the axis. In lenses the spot diagram has been useful in evaluating image quality. In axicons a corresponding line diagram where lines take the place of dots is useful. In general, axicon instruments correspond to the usual optical instruments. For example, an axicon may be used as an objective to form a telescope. The resulting axicon telescope may be used in aligning machinery such as paper mills. Similarly, an axicon autocollimator may be used to precisely set mirrors perpendicular to a line. One form of axicon microscope has been tried out for the special purpose of locating the position of shiny surfaces without touching them. A most useful form of optical aligner is the reflection cone axicon. It is used as a straight edge. One example is a reflecting cone of 6 in. diam and maximum range of 40 ft with precision of 5 or 6 wavelengths over the entire range. Another example is a 5 in. diam cone with a range of 10 ft and precisions of about 1 wavelength. In this case the use of a suitable radius for the reflecting surface had the effect of making the image brightness substantially uniform over the 10 ft range. Photo cell pickup has been shown to be successful with very high precisions of setting. This opens the way for automatic machine guiding to very high precisions.
JOHN H. MCLEOD, "Axicons and Their Uses," J. Opt. Soc. Am. 50, 166-166 (1960)